1. Field of Invention
This invention relates to a lamination device to laminate a material to be formed by heating and pressurizing under a vacuum atmosphere.
2. Background of Related Art
For instance, in the case of manufacturing a printed circuit board, there is a process where an insulating substrate made from thermosetting resin such as a phenol resin or an epoxy resin or an insulating base film having flexibility made from a thermoplastic resin such as a polyimid is laminated with an electric conductive layer such as copper foils patterned or to be etched at a later process (hereinafter, the former is referred to merely as lamination substrate and the latter is referred to as flexible lamination substrate). In the case of forming a lamination substrate, an insulating substrate and copper foils are heated and pressurized under a vacuum atmosphere, the insulating substrate is plasticized due to a chemical reaction of thermosetting resin and laminated with the copper foils by adhesion, and further chemical reaction causes the insulating substrate adhered with the copper foils to be hardened. Further, in the case of forming a flexible laminating substrate too similarly an insulating base film and copper foils are heated and pressurized under a vacuum atmosphere and make the insulating base film plasticized to be laminated with copper foils due to adhesion. That is, in a process where an electric conductive layer such as copper foils is laminated, a material to be formed itself such as insulating substrate made of a thermoplastic resin or an insulating base film becomes an adhesive.
Further, to these lamination substrate and flexible lamination substrate, there is, in order to protect copper foils laminated from etching, metal plating and soldering, a process of heat-pressure-adhering on the electric conductive layer surface laminated with a film-like photoresist-forming layer made of a supporting film and a photo-sensitive layer. The photoresist-forming layer becomes adhesive by being heated and is laminated on the surface of copper foils under being pressurized.
In thus formed printed circuit boards, in recent years integrated density has become higher and in accordance with the development of surface treatment thereof the constitution thereof has been also changed. Eventually, a multiple layer printed circuit board or a multiple layer flexible printed circuit board having more than three layers of electric conducting patterns including a surface conducting layer has been often used. In the case where such multiple layer printed circuit board is manufactured, a build-up method has been employed, in which, to the conducting layer of the lamination substrate or the flexible lamination substrate, further an insulating substrate or an insulating base film and a conducting layer are in turn laminated.
By the way, at the time of carrying out the process of the above lamination of the conducting layer or the heat-pressure adhering of a film-like photoresist-forming layer, bubbles consisting of some volatile ingredients of a material to be formed are apt to remain between the lamination substrate or the flexible lamination substrate and the copper foils or between the laminated copper foils and the film-like photoresist-forming layer and generate voids. Thus generated voids may swell at the time of a post-treatment under a high temperature, for example a molten solder bath etc., and give some damages to the laminated copper foils and the film-like laminated photoresist-forming layer, so that there is an anxiety to cause malfunction of the protection and insulation, further including electric conductivity.
From the above, in the case where every lamination is carried out in every kind of material to be formed by heating and pressurizing, in order to avoid the generation of voids, a lamination method under a vacuum atmosphere has been conventionally carried out.
As a conventional vacuum lamination device for laminating a material to be formed which consists of a plurality of plate-like, sheet-like or film-like materials, as disclosed in the Japanese patent laid-open publication Nos. 295218/1988 and 299895/1988, it has been known that a cylindrical rubber is provided inside a heating vessel or a rubber sheet is provided inside a vacuum chamber which is free of opening and closing, and a vacuum pump is connected inside the cylindrical rubber or between the rubber sheets. In these vacuum lamination devices, a material to be formed is disposed inside the cylindrical rubber or between rubber sheet, a vacuum forming chamber is formed by sealing the cylindrical rubber or the rubber sheet and the vacuum forming chamber is depressurized to pressurize the material to be formed by the cylindrical rubber or the rubber sheet. In the Japanese patent laid-open publication No. 295218/1988, a stage material is heated by the heating vessel connected to the heating device. Further, in the Japanese patent laid-open publication No. 299895/1988, a stage material is heated by the stationary chamber and the movable chamber heated by a heating mechanism.
Further, as a conventional vacuum lamination method, as disclosed in the Japanese patent publication No. 13341/1980, it has been known that, by making a photoresist-forming layer bonded on a film supporter arranged adjacent to the surface of a circuit board, depressurizing the absolute pressure on the area between the surface of the circuit board and the photoresist-forming layer and on the film supporter to less than 1 atmosphere, pressurizing the film supporter which functions as a pressure transmitting layer to pressurize the photoresist-forming layer on the surface of the circuit board, and softening the photoresist-forming layer by heating, the laminating is carried out.
Further, as another conventional vacuum lamination device, for instance, as disclosed in the Japanese utility model publication No. 52200/1992, a vacuum hot press has been known, in which a plurality of heating plates are disposed between a stationary base and a movable base provided, which is free of opening and closing to the stationary base and a vacuum chamber is formed by enclosing a space where the movable base displaces. In such a vacuum hot press, in general, in every heating plate a temperature regulating fluid passage is formed, and, by passing a heating medium such as pressured vapor or heated oil through the passage, every material to be formed inserted between the respective heating plates is pressurized and heated simultaneously. And, by passing a coolant such as cooling water interchangeably with a heating medium through this temperature regulating fluid passage or through another temperature regulating fluid passage for supplying the coolant provided on each heating plate, a heated material to be formed is cooled.
By the way, in the device (hereinafter referred to as vacuum laminator) used in the vacuum lamination method of the Japanese patent laid-open publication Nos. 295218/1988, 299895/1988 or the Japanese patent publication No. 13341/1980, there have been problems in which, before a thermosetting resin is pressurized, due to a heat transmission and a radiation heat in the chamber, a hardening reaction advances, so that a malfunction in adhering to a material to be formed such as copper foils is generated and eventually an adhering strength is not guaranteed.
Further, since the material to be formed which was heated by the heating device or the heating mechanism is made to be gradually cooled to the temperature, which makes the material to be formed stable, even after a lamination process is completed, the heat at the time of being heated remains in the material to be formed, in addition, since a coefficient of thermal expansion is different between the electric conducting layer such as copper foils and, the insulating substrate or the insulating base film made of a thermosetting resin or the film-like photoresist-forming layer, there has been a problem to generate defects such as wrinkles, drawn portions and deformation due to thermal shrinking by an abrupt and uneven descent of the temperature.
Further, in the case where the material to be formed is highly dependent on the temperature like the film-like photoresist-forming layer which bears adhesive property by being heated as mentioned above, prior to being fallen in a vacuum atmosphere a portion getting in touch with the material is adhered and there has happened to generate a problem in which malfunction occurs in air sucking between the laminated copper foils and the film-like photoresist-forming layer. In addition, there has happened to generate a problem of much advancing in plasticizing before being pressurized, which causes the lamination to generate wrinkles or decrease positioning precision. And, these problems cause the yield rate of the products to decrease.
On the other hand, in the vacuum hot press as disclosed in the Japanese utility model publication No. 52200/1992, since the heating medium or cooling medium is supplied through the temperature regulating fluid passage provided in each heating plate, heat capacity is great, and the molding cycle can not be shortened, further there has been a problem in which the heat efficiency is inferior and expensive in cost and the increase of productivity can not be realized.